1. Field of the Invention
This invention relates to the recovery of tertiary butyl hydroperoxide and tertiary butyl alcohol from a heavy distillation fraction comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and impurities, including dissolved molybdenum catalyst.
More particularly, this invention relates to the recovery of tertiary butyl hydroperoxide and tertiary butyl alcohol from a heavy distillation fraction comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and impurities, including dissolved molybdenum catalyst which remains after a distillate propylene fraction, a distillate propylene oxide fraction and a distillate tertiary butyl alcohol fraction are removed, by distillation, from the reaction product formed by the reaction of excess propylene with tertiary butyl hydroperoxide in solution in tertiary butyl alcohol in the presence of a soluble molybdenum catalyst.
Still more particularly, this invention relates to the separation of a heavy distillation fraction comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and impurities, including dissolved molybdenum catalyst in appropriate vacuum evaporation equipment such as a thin film evaporator, a wiped film evaporator, a forced circulation evaporator, etc., under evaporation conditions including a temperature of about 25.degree. to about 160.degree. C. and a pressure of about 2 to about 200 mm Hg. into a lighter condensate fraction comprising about 60 to about 95 wt. % of the heavy distillation fraction and containing from about 70 to about 95 wt. % of tertiary butyl alcohol, about 1 to about 20 wt. % of the tertiary butyl hydroperoxide and from about 15 to about 3 wt. % of impurities and also into a clear liquid heavier residue fraction comprising tertiary butyl alcohol, tertiary butyl hydroperoxide and impurities including substantially all of the soluble molybdenum catalyst originally contained in the heavy liquid fraction.
In the past, the heavy distillation fraction remaining after removing unreacted propylene, propylene oxide and tertiary butyl alcohol from the reaction product formed by the reaction of excess propylene with tertiary butyl hydroperoxide in solution in tertiary butyl alcohol in the presence of a soluble molybdenum catalyst has generally been considered to be a "waste" product to be treated for the recovery of molybdenum therefrom in order to permit use of the molybdenum-free components as fuel.
It is surprising that evaporation conditions have been discovered that are sufficiently mild to permit the evaporation of tertiary butyl hydroperoxide and tertiary butyl alcohol in the presence of comparatively large quantities of molybdenum and organic acids without the concommitment dehydration of the tertiary butyl alcohol to isobutylene and water and the decomposition of the tertiary butyl hydroperoxide to tertiary butyl alcohol and water.
It is also surprising that the same evaporation conditions are severe enough to permit the substantially quantitative concentration of molybdenum in a heavier bottoms or residue fraction that remains liquid and easy to handle.
2. Prior Art
A process for the coproduction of an epoxide such as propylene oxide with an alcohol such as tertiary butyl alcohol is disclosed and described in Kollar U.S. Pat. Nos. 3,350,422 and 3,351,635. When the olefin is propylene and the hydroperoxide is tertiary butyl hydroperoxide, the principal reaction products are propylene oxide and tertiary butyl alcohol.
Numerous patents have issued describing improvements in the process, such as Russell U.S. Pat. No. 3,418,340, Stein et al. U.S. Pat. No. 3,849,451 and Wu et al. U.S. Pat. No. 4,217,287.
Numerous patents have also issued which are directed to the preparation of molybdenum catalysts useful in catalyzing the reaction of propylene with tertiary butyl hydroperoxide to form propylene oxide and tertiary butyl alcohol such as Mattucci et al. U.S. Pat. No. 3,668,227, Lines et al. U.S. Pat. No. 4,009,122, Brewster U.S. Pat. No. 4,192,578 and Marquis et al. U.S. Pat. Nos. 4,650,886, 4,654,427, 4,703,027 and 4,758,681.
In accordance with molybdenum catalyzed epoxidation processes such as those described in the references, propylene and tertiary butyl hydroperoxide are reacted in solution in tertiary butyl alcohol in an epoxidation reaction zone in the presence of a soluble molybdenum catalyst under epoxidation reaction conditions to form an epoxidation reaction product which is discharged from the epoxidation reaction zone and charged to a distillation zone containing an appropriate number of distillation columns wherein the epoxidation reaction product is typically resolved into a distillate propylene recycle fraction, a distillate propylene oxide product fraction and a distillate tertiary butyl alcohol fraction. A heavy liquid distillation fraction, normally a bottoms fraction, will remain after the separation of the unreacted propylene, the propylene oxide and the tertiary butyl alcohol which will be composed of unreacted tertiary butyl hydroperoxide, tertiary butyl alcohol, impurities and the dissolved molybdenum catalyst.
Levine U.S. Pat. No. 3,819,663 is directed to a method for treating a heavy distillation fraction of this nature in order to recover the molybdenum in the concentrated bottoms fraction for recycle to the epoxidation reaction zone as makeup catalyst.
Levine conducts his wiped-film evaporation process under conditions including a temperature of about 550.degree.-650.degree. F. (about 273.degree. to about 330.degree. C.) at atmospheric pressure to obtain his desired residual fraction for recycle as catalyst makeup and a distillate fraction comprising about 85% or more of the heavy distillation fraction.
Moreover, the high temperatures used by Levine and the concentration of molybdenum in his wiped film evaporator are such that at least partial dehydration of the tertiary butyl hydroperoxide and tertiary butyl alcohol will occur. One of Levine's objectives is the provision of a molybdenum-free overhead that can be burned as a fuel. Although Levine states that the distillate fraction can be worked up for recovery of individual components contained therein, he neither teaches nor describes any technique or equipment that could be used for this purpose.
In U.S. Pat. No. 4,445,283, Sweed describes a process for evaporation of the heavy distillation fraction in order to provide a spent catalyst solution containing between about 0.1 and 2.0 wt. % of molybdenum. The evaporation is accomplished under special evaporation conditions at a pressure of less than about 400 mm Hg in a circulation evaporator and heating means designed so that the feed to the evaporator is not preheated under pressure.
Thornton et al. U.S. Pat. No. 4,584,413 discloses a process for removing contaminating quantities of primary and secondary alkyl hydroperoxides from tertiary butyl hydroperoxide formed by the oxidation of isobutane by mixing an isobutane oxidation product such as one comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and oxygenated by-products including primary and secondary alkyl hydroperoxides with an aqueous solution of an alkali metal or alkaline earth metal hydroxide followed by distillation of the mixture to obtain a tertiary butyl alcohol fraction and a two-phase tertiary butyl hydroperoxide azeotrope fraction, the tertiary butyl hydroperoxide phase of which is neutralized in order to provide a more purified tertiary butyl hydroperoxide product.